Potassium is an important fertilizer and it is found in nature as salts such as sylvinite (NaCl. KCl), carnallite (KCl.MgCl2.6H2O) or kainite (KCl.MgSO4.3H2O). Most of the potassium made available for fertilizer uses is in the form of potassium chloride. But with intensive cultures, the chlorine combined with the potassium in potassium chloride has undesirable effects on soil, and therefore a chlorine-free potassium is desirable, generally a sulfate of potassium and magnesium. In many instances, however, pure potassium sulfate, K2SO4, would be desirable because of its high potassium content.
This has led to the development of techniques for the production of potassium sulfate from naturally occurring sources of potassium. One of these methods (Treatise on Inorganic Chemistry, H. Remy, Vol. 1, p. 199, Elsevier Publishing Co., 195) calls for the treatment of schönite with a solution of KCl, according to the following reaction:K2SO4.MgSO4.6H2O+2KCl→2K2SO4+MgCl2.6H2O
In practice, it has been found very difficult to obtain a potassium sulfate essentially free of magnesium chloride with this approach, the mother liquor of this crystallization leaving several percent of chloride ions in the end product K2SO4.
More recently, a thermal method (Mannheim process, Chemical Process Industries, R. N. Shreeve, McGraw-Hill, 3rd ed., 1967, p. 346) has been implemented to obtain potassium sulfate directly by the reaction of potassium chloride with sulfuric acid, as follows:2KCl+H2SO4→K2SO4+2HCl
This reaction is conducted at 450° C. in silica reactors, with very poor thermal efficiencies and fast degradation of the reactor, the species involved, sulfuric acid, potassium hydrogen sulfate and potassium sulfate being highly corrosive.
Another existing approach to obtain potassium sulfate from potash and sulfuric acid calls upon the use of ion exchange resin (Big Quill Resources Inc. website homepage: www.bigquill.com). This approach leads to a multiplicity of solutions, which renders this approach costly and complex.
Therefore, there is still a need in the art for a method and a system for the production of potassium sulfate.